Magnetic disk apparatus

ABSTRACT

According to one embodiment, there is provided a magnetic disk apparatus having a magnetic disk having magnetic dot lines each including magnetic dots arrayed at equal intervals in a down track direction, and a read/write head which uses a plurality of adjacent magnetic dot lines as one track and sequentially performs read and write on the magnetic dots included in the magnetic dot lines constituting the track, in which the magnetic dots included in each of the magnetic dot lines in each track of the magnetic disk are displaced in the down track direction from the magnetic dots included in the adjacent dot line in the track depending on a possible skew angle between the read/write head and the track so that the magnetic dots are sequentially accessed by the read/write head.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2006-182737, filed Jun. 30, 2006, theentire contents of which are incorporated herein by reference.

BACKGROUND

1. Field

One embodiment of the present invention relates to a magnetic diskapparatus, and in particular, to a magnetic disk apparatus using a bitpatterned medium.

2. Description of the Related Art

In current magnetic disk apparatuses (hard disk drives), bits arewritten to a recording layer with a magnetic head. For magnetic disks inthese magnetic disk apparatuses, problems such as the interferencebetween adjacent tracks and thermal fluctuation resistance have becomeserious.

Proposals have been made of bit patterned media in which a magneticmaterial is processed into arrayed magnetic dots separated from oneanother each of which is used as one bit. Such bit patterned media areexpected to solve the problems such as the interference between adjacenttracks and thermal fluctuation resistance.

In current magnetic disks, one bit written by a magnetic head has anaspect ratio of about 4 to 7 and is longer in the cross track directionthan in the down track direction. In such a bit pattern, if a bit aspectratio is 4, a bit pitch is 25 nm, and the ratio of the bit length to thelength of a non-recording area in the down track direction is 2:1, theinterval between the bits is about 8 nm.

However, when an attempt is made to manufacture bit patterned mediahaving a bit pattern equivalent to that of the current magnetic disks,forming magnetic dots of a high aspect ratio is very difficult and isimpractical.

Thus, a proposal has been made of a bit patterned medium in which aself-assembling material is used to arrange magnetic dots in the downtrack direction to form magnetic dot lines so that magnetic dots in eachmagnetic dot line are displaced from those in the adjacent magnetic dotline by a ½ pitch. In addition, a proposal has been made that read andwrite be sequentially performed on magnetic dots included in a pluralityof dot lines used as one track (Jpn. Pat. Appln. KOKAI Publication No.2002-279616).

This bit patterned medium enables read and write similarly to thecurrent magnetic disks. This eliminates the need to form magnetic dotsof a high aspect ratio and provides a sufficient interval between themagnetic dots.

However, in this bit patterned medium, the amount by which the magneticdots included in each magnetic dot line are displaced from thoseincluded in the adjacent magnetic dot line is fixed to a ½ pitch. Thus,the bit patterned medium disadvantageously cannot deal with a skew anglethat may occur when the head accesses the inner or outer peripheral sideof the magnetic disk.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A general architecture that implements the various feature of theinvention will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the invention and not to limit the scope of theinvention.

FIG. 1 is a perspective view of a magnetic disk apparatus (hard diskdrive) according to an embodiment of the present invention;

FIGS. 2A and 2B are diagrams showing a skew angle in the magnetic diskapparatus in FIG. 1;

FIG. 3 is a diagram schematically showing the shape of bits recorded ina current magnetic disk;

FIGS. 4A and 4B are plan views showing magnetic dots formed in amagnetic disk according to the embodiment of the present invention; and

FIG. 5 is a plan view showing magnetic dots formed in a magnetic diskaccording to another embodiment of the present invention.

DETAILED DESCRIPTION

Various embodiments according to the invention will be describedhereinafter with reference to the accompanying drawings. In general,according to one embodiment of the present invention, there is provideda magnetic disk apparatus comprising: a magnetic disk comprisingmagnetic dot lines each including magnetic dots arrayed at equalintervals in a down track direction; and a read/write head which uses aplurality of adjacent magnetic dot lines as one track and sequentiallyperforms read and write on the magnetic dots included in the magneticdot lines constituting the track, wherein the magnetic dots included ineach of the magnetic dot lines in each track of the magnetic disk aredisplaced in the down track direction from the magnetic dots included inthe adjacent dot line in the track depending on a possible skew anglebetween the read/write head and the track so that the magnetic dots aresequentially accessed by the read/write head.

FIG. 1 is a perspective view of a magnetic disk apparatus (hard diskdrive) according to an embodiment of the present invention. Thismagnetic recording/reproduction apparatus comprises a chassis 50, amagnetic disk 51, a head slider 56 including a magnetic head, a headsuspension assembly (a suspension 55 and an actuator arm 54) supportingthe head slider 56, a voice coil motor (VCM) 57, and a circuit board.

The magnetic disk (bit patterned medium) 51 is fitted on the spindlemotor 52 and rotated so that various digital data can be recorded in themagnetic disk according to a perpendicular magnetic recording system.The magnetic head incorporated in the head slider 56 is of what is aso-called integrated type and includes a write head with a single-polestructure and a read head using a shield MR reproducing element (a GMRfilm, a TMR film, or the like). The suspension 55 is held at one end ofthe actuator arm 54 to support the head slider 56 opposite the recordingsurface of the magnetic disk 51. The actuator arm 54 is attached to thepivot 53. The voice coil motor (VCM) 57 is provided at the other end ofthe actuator arm 54. The voice coil motor (VCM) 57 drives the headsuspension assembly to locate the magnetic head at any radial positionon the magnetic disk 51. The circuit board comprises a head IC togenerate, for example, driving signals for the voice coil motor (VCM)and control signals for controlling read and write operations performedby the magnetic head.

A possible skew angle in the magnetic disk apparatus in FIG. 1 will bedescribed with reference to FIGS. 2A and 2B. FIG. 2A is a plan viewshowing the positional relationship between the magnetic disk 51 andactuator arm 54 and head slider 56 in the magnetic disk apparatus inFIG. 1. The actuator arm 54 is driven by the voice coil motor to move ina radial direction of the magnetic disk 51 so as to draw a circular arcover the disk. As shown in FIG. 2B, for example, when the head slider 56is moved to above the outer periphery of the magnetic disk 51, the headslider 56 is located angularly to recording tracks. In this case, theskew angle θ is defined as an angle formed between the direction of thelonger side of the read head (that is parallel to the surface of the GMRfilm, the TMR film, or the like) and the cross track direction.

FIG. 3 schematically shows the shape of bits recorded in currentmagnetic disks. FIG. 3 shows two lines of bit patterns in which bits 11included in each line are recorded at a bit aspect ratio of 4 and a bitpitch of 25 nm. In this case, if the ratio of the bit 11 to thenon-recording area in the down track direction is set at 2:1, theinterval between the adjacent bits 11 becomes about 8 nm. It isdifficult to process a magnetic layer to form bits in a form similar tothat described above, which constitute magnetic dots.

FIGS. 4A and 4B are plan views showing magnetic dots 21 formed in themagnetic disk according to the embodiment of the present invention. Inthis magnetic disk, two magnetic dot lines (N=2) are used as one track.FIG. 4A shows magnetic dots in an area with a skew angle of zero. FIG.4B shows magnetic dots in an area with a skew angle θ.

As shown in FIG. 4A, a track pitch is defined as T, and a bit pitchobtained when the skew angle is zero is defined as B. Magnetic dots 21included in each magnetic dot line are arranged at a pitch NB. In thiscase, if the bit pitch is set at 25 nm and the ratio of a magneticmaterial to a nonmagnetic material in the down track direction is set at2:1 as in the case of the current magnetic disks, the interval betweenthe magnetic dots 21 can be made N times as large as that in the priorart. That is, for N=2, the interval can be doubled to 16 nm.

In the magnetic disk according to the embodiment of the presentinvention, in an area in which the head 31 has the skew angle θ, theamount by which the magnetic dots 21 included in each of the magneticdot lines in each track are displaced from those included in theadjacent magnetic dot line in that track is adjusted depending on theskew angle θ as shown in FIG. 4B. Specifically, the magnetic dotsincluded in the n-th (n is an integer from 0 to N−1) magnetic dot linein each track are displaced in the down track direction from thoseincluded in the 0-th magnetic dot line in that track by a displacementΔB represented by the following formula:ΔB=B−(Tn/N)tan θ.

When the amount by which the magnetic dots 21 included in each of themagnetic dot lines in each track are thus displaced from those includedin the adjacent magnetic dot line in that track is adjusted depending onthe skew angle θ, the magnetic dots 21 included in the two magnetic dotlines are alternately and sequentially accessed by the head 31 as shownin FIG. 4B. This enables an operation equivalent to achievement of ahigh bit aspect ratio during read and write performed on each track.

FIG. 5 is a plan view showing the magnetic dots 21 formed on a magneticdisk according to another embodiment of the present invention. In thismagnetic disk, three magnetic dot lines (N=3) are used as one track.Also in this example, the amount by which the magnetic dots 21 includedin each of the magnetic dot lines in each track are displaced from thoseincluded in the adjacent magnetic dot line in that track is adjusteddepending on the skew angle θ.

In both FIGS. 4 and 5, the interval between the magnetic dot lines ineach track is preferably shorter than that between the adjacent tracks.

Now, a brief description will be given of a process of manufacturing amagnetic disk according to the embodiment of the present invention. Theprocess of manufacturing a magnetic disk comprises a transfer step, amagnetic material processing step, and a finishing step. The descriptionwill start with the manufacture of a stamper used as a template forpatterns used in the transfer step.

The step of manufacturing a stamper is divided into pattern drawing,development, electroforming, and finishing. In pattern drawing, a resistis applied to a master. A master-rotating electron-beam exposureapparatus is used to direct-write areas of the magnetic disk where anonmagnetic material is to be formed from the inner circumference toouter circumference. The disk is subjected to development and then to aprocess such as reactive ion etching (RIE) to form a master having theresist with patterns of recesses and protrusions. A Ni thin film isdeposited on the master to make the disk conductive. The Ni film iselectroformed and then released. Finally, the master is punched atportions corresponding to an inner diameter and an outer diameter. A Nistamper is thus formed. The stamper has protrusions corresponding toareas of the magnetic disk where a nonmagnetic material is to be formed.The stamper is used to manufacture a bit patterned medium.

In the transfer step, a double-side simultaneous transferring imprintapparatus is used to transfer patterns of the stamper by imprintlithography. Specifically, spin-on-glass (SOG) is applied to bothsurfaces of the perpendicular recording disk. The disk is chucked at itscentral hole and sandwiched between two stampers provided for the rearand front surface, respectively, of the disk. The entire surface of thedisk is uniformly pressed to transfer the recesses and projections ofthe stampers to the resist surface. The transfer step provides theresist with the recesses corresponding to the areas of the magnetic diskwhere the nonmagnetic material is to be formed.

In the magnetic material processing step, resist residues remaining inthe recesses of the resist are removed to expose the surface of themagnetic material in the areas where the nonmagnetic material is to beformed. In this stage, the protrusions made of SiO₂ are formed on theareas where the magnetic layer is to be left. Then, ion milling isperformed using the protrusions of SiO₂ as a mask to remove the magneticlayer exposed from the recesses between the protrusions of SiO₂ to formmagnetic dots having desired patterns. Further, sputtering is performedto form SiO₂ with a sufficient thickness. The SiO₂ is then etched backto the surface of the magnetic layer so as to fill the recesses with thenonmagnetic material (SiO₂) for flattening.

In the finishing step, abrasive finishing is performed to furtherincrease the flatness of the surface. A DLC protective layer is thenformed and a lubricant is applied to this layer. Thus, the bit patternedmedium according to the embodiment of the present invention can bemanufactured.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the inventions. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

1. A magnetic disk apparatus comprising: a magnetic disk comprisingmagnetic dot lines each including magnetic dots arrayed at equalintervals in a down track direction; and a read/write head which uses aplurality of adjacent magnetic dot lines as one track and sequentiallyperforms read and write on the magnetic dots included in the magneticdot lines constituting the track, wherein the magnetic dots included ineach of the magnetic dot lines in each track of the magnetic disk aredisplaced in the down track direction from the magnetic dots included inthe adjacent dot line in the track depending on a possible skew anglebetween the read/write head and the track so that the magnetic dots aresequentially accessed by the read/write head.
 2. The magnetic diskapparatus according to claim 1, wherein N lines of magnetic dot linesare used as one track in the magnetic disk, and wherein, assuming that atrack pitch is T, a bit pitch at zero skew angle is B, and a skew angleis θ, the magnetic dots included in each magnetic dot line are arrayedat a pitch NB in the down track direction, and the magnetic dotsincluded in an n-th (where n is an integer from 0 to N−1) magnetic dotline in each track are displaced in the down track direction from themagnetic dots included in a 0-th magnetic dot line in the track by adisplacement represented by the following formula: B−(Tn/N)tan θ.
 3. Themagnetic disk apparatus according to claim 1, wherein the intervalbetween the magnetic dot lines in each track is shorter than an intervalbetween the tracks.